1. Field of the Invention
The present invention relates to rotors and more specifically to the incorporating therein of inherently strong, highly damped, yet light weight characteristics of fiber reinforced plastic (FPR) composite material for vibro-acoustic applications.
2. Description of the Prior Art
Fiber reinforced plastic composites have both performance and fabrication characteristics which are beneficial to all generically related rotor applications in both air and water flow. When used in the fabrication of rotors, relatively low density composite materials reduce overall weight and inertial loading. Superior vibration damping performance is desirable in order to reduce noise and fatigue due to vibration in rotor applications. The prior art shows that highly damped composites are feasible and effective as materials of construction for marine propulsors and other rotor applications. However, the low density of composites accentuates the low structural impedance in the tip region of rotor blades so that the rotors are easily excited. This offsets the potential advantage of high damping, since minimizing the vibration response of a rotor to flow excitation requires high values for both material density and mechanical damping. Nevertheless, the desirable quality of low composite material density in terms of weight saving may be maintained, and the acoustically detrimental quality thereof may be reduced, by an appropriate tailoring of mass distribution in a rotor via localization of the high density material in the tip region.
U.S. Pat. No. 4,097,193 illustrates an elastomeric damping arrangement for damping vibrations of a structural member, such as a vibration prone airfoil, particularly a helicopter rotor blade tending to vibrate under dynamic deformations.
U.S. Pat. No. 4,797,066 illustrates a propeller blade at an increased service load automatically optimizes its pitch, thus reducing or preventing cavitation wherein flexibility is obtained for the propeller utilizing plastic materials have anisotropic properties, i.e. from materials with different physical characteristics in different directions.